Review of the Prior Art
Substantial reserves of hydrocarbons, i.e., oil and gas, are known to lie beneath the floors of the oceans of the world. Many of these reserves lie under shallow waters, as under continental shelves relatively close to shore. Much equipment and various procedures have been developed over the years at great cost to tap these shallow-water reserves. There is presently a significant worldwide inventory of equipment useful to drill wells in shallow waters and to produce oil and gas from such wells. Production equipment for use with offshore wells most commonly involves a tower or platform erected on the ocean floor and extending to above the ocean surface.
Shallow water oil and gas reserves are being depleted steadily. The search for offshore oil and gas is moving into deeper and deeper water farther and farther from shore. Substantial reserves have been located under waters 1000 feet (303 meters) or more in depth. Such depths are beyond the economic threshold of development, assuming the use of existing equipment and procedures designed and created for use in shallower waters; in some instances, newly discovered subsea hydrocarbons reserves are under waters of such great depth as to be beyond the limits of present technology, irrespective of cost.
Rigid bottom-supported structures, such as have been developed for use in the North Sea, are extremely expensive; their costs increase exponentially with increased water depth. The use of existing technology and equipment is presently limited to waters somewhat over 1000 feet (303 meters) deep or less.
Current known efforts to design hydrocarbons production systems for use in deep water (i.e., waters deeper than about 1000 feet or about 300 meters) focus predominantly upon the use of subsea completion systems which involve expensive and untested (in terms of reliability) control equipment on the sea floor. In deep water, such equipment is costly and often hazardous to maintain.
It is thus apparent that a need exists for new technology, equipment and procedures effective at reasonable cost to develop and produce subsea hydrocarbons reserves lying under waters 1000 feet (303 meters) or more in depth.